A common mechanism behind multidrug resistance is the overexpression of a plasma membrane glycoprotein (P-glycoprotein) in resistant cells. P- glycoprotein is believed to function as an energy-driver drug efflux pump. The overall objectives of this research proposal are to investigate the effects of phosphorylation and N-linked glycosylation on the structure, function and regulation of this drug efflux pump. The long term goals are the use the information acquired in these studies to develop new therapeutic protocols to reverse or overcome drug resistance. The major objectives of this proposal are to: a) Use fast atom bombardment mass spectrometry (FASMS) to map the sites of phosphorylation and N-linked glycosylation in P-glycoprotein. b) Use site specific mutagenesis to determine which phosphorylation(s) site(s) is(are) important for the regulation of P-glycoprotein function. c) Determine by transfection into glycosylation defective cells the extent oligosaccharides contribute to the functional/structural properties of P- glycoprotein.